Best foot forward would be for Thanos to show up in Thor 2 and, in the process, kill Odin. I know Odin is stronger than Thanos, but Thanos is cunning and smart, so he'll find a way to win, leading to a battle between Thanos and the team in Avengers 2. Thanos vs. Thor + Belt of Strength would be a dream fight. Around 10-15 minutes would be beyond awesome.